Method of making a kink resistant stent-graft

ABSTRACT

A stent-graft including a stent member having an inner surface and an outer surface, a generally tubular graft member and a coupling member that couples the stent member to the graft member. The coupling member, which is the preferred embodiment is in the form of a ribbon, covers only a portion of the inner or outer surface of the stent member and secures the stent member and graft member to one another. Alternatively, the coupling member can be to described as interconnecting less than entirely the inner or outer surface of the graft member to the stent member. With this construction, regions of the stent member do not interfere with the coupling member. Shear stresses between the stent member and the coupling member and the risk of tearing the graft or coupling member or delamination therebetween may be reduced as compared to a fully enveloped stent member. This construction also provides improved flexibility and kink resistance.

CONTINUING DATA

This application is a divisional application of U.S. application Ser.No. 08/896,805, filed Jul. 18, 1997, now U.S. Pat. No. 6,042,605, whichis a continuation-in-part of Ser. No. 08/572,548, filed Dec. 14, 1995,now abandoned, the entirety of which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to implants for repairing ducts andpassageways in the body. More specifically, the invention relates to anexpandable stent-graft.

BACKGROUND OF THE INVENTION

Treatment or isolation of vascular aneurysms or of vessel walls whichhave been thinned or thickened by disease has traditionally beenperformed via surgical bypassing with vascular grafts. Shortcomings ofthis procedure include the morbidity and mortality associated withsurgery, long recovery times after surgery, and the high incidence ofrepeat intervention needed due to limitations of the graft or of theprocedure.

Vessels thickened by disease are currently sometimes treated lessinvasively with intraluminal stents that mechanically hold these vesselsopen either subsequent to or as an adjunct to a balloon angioplastyprocedure. Shortcomings of current stents include the use of highlythrombogenic materials (stainless steels, tantalum, ELGILOY) which areexposed to blood, the general failure of these materials to attract andsupport functional endothelium, the irregular stent/vessel surface thatcauses unnatural blood flow patterns, and the mismatch of mechanicalcompliance and flexibility between the vessel and the stent.

Various attempts have been made to provide a nonthrombogenicblood-carrying conduit. Pinchuk, in U.S. Pat. Nos. 5,019,090, 5,092,887,and 5,163,958, suggests a spring stent which appears tocircumferentially and helically wind about as it is finally deployedexcept, perhaps, at the very end link of the stent. The Pinchuk '958patent further suggests the use of a pyrolytic carbon layer on thesurface of the stent to present a porous surface of improvedantithrombogenic properties.

U.S. Pat. No. 5,123,917, to Lee, suggests an expandable vascular grafthaving a flexible cylindrical inner tubing and a number of “scaffoldmembers” which are expandable, ring-like and provide circumferentialrigidity to the graft. The scaffold members are deployed by deformingthem beyond their plastic limit using, e.g., an angioplasty balloon.

A variety of stent-graft designs also have been developed to improveupon simple stent configurations. Perhaps the most widely knownstent-graft is shown in Ersek, U.S. Pat. No. 3,657,744. Ersek shows asystem for deploying expandable, plastically deformable stents of metalmesh having an attached graft through the use of an expansion tool.

Palmaz describes a variety of expandable intraluminal vascular grafts ina sequence of patents: U.S. Pat. Nos. 4,733,665; 4,739,762; 4,776,337;and 5,102,417. The Palmaz '665 patent suggests grafts (which alsofunction as stents) that are expanded using angioplasty balloons. Thegrafts are variously a wire mesh tube or of a plurality of thin barsfixedly secured to each other. The devices are installed, e.g., using anangioplasty balloon and consequently are not seen to be self-expanding.The Palmaz '762 and '337 patents appear to suggest the use ofthin-walled, biologically inert materials on the outer periphery of theearlier-described stents. Finally, the Palmaz '417 patent describes theuse of multiple stent sections each flexibly connected to its neighbor.

Rhodes, U.S. Pat No. 5,122,154, shows an expandable stent-graft made tobe expanded using a balloon catheter. The stent is a sequence ofring-like members formed of links spaced apart along the graft. Thegraft is a sleeve of a material such as an expanded polyfluorocarbon,expanded polytetrafluoroethylene available from W. L. Gore & Associates,Inc. or IMPRA Corporation.

Schatz, U.S. Pat. No. 5,195,984, shows an expandable intraluminal stentand graft related in concept to the Palmaz patents discussed above.Schatz discusses, in addition, the use of flexibly-connecting vasculargrafts which contain several of the Palmaz stent rings to allowflexibility of the overall structure in following curving body lumen.

Cragg, “Percutaneous Femoropopliteal Graft Placement”, Radiology, vol.187, no. 3, pp. 643-648 (1993), shows a stent-graft of a self-expanding,nitinol, zig-zag, helically wound stent having a section ofpolytetrafluoroethylene tubing sewed to the interior of the stent.

Cragg (European Patent Application 0,556,850) discloses an intraluminalstent made up of a continuous helix of zig-zag wire and having loops ateach apex of the zig-zags. Those loops on the adjacent apexes areindividually tied together to form diamond-shaped openings among thewires. The stent may be made of a metal such as nitinol (col. 3 lines15-25 and col. 4, lines 42+), and may be associated with a“polytetrafluoroethylene (PTFE), dacron, or any other suitablebiocompatible material”. Those biocompatible materials may be inside thestent (col. 3 lines 52+) or outside the stent (col. 4, lines 6+).

WO93/13825 to Maeda et al. discloses a self-expanding stent having awire bent into an elongated zig-zag pattern and helically would about atubular shape interconnected with a filament. A sleeve may be attachedto the outer or inner surface of the stent.

PCT application publication WO/95/05132 discloses a stent-graft with atubular diametrically adjustable stent.

There is a need for an alternate stent-graft construction that exhibitsexcellent kink resistance and flexibility.

SUMMARY OF THE INVENTION

The present invention involves a stent-graft including a stent memberhaving an inner surface and an outer surface, a generally tubular graftmember and a coupling member that couples the stent member to the graftmember. The coupling member, which in the preferred embodiment is in theform of a ribbon, covers only a portion of at least one of the inner orouter surface of the stent member and secures the stent member and graftmember to one another. Alternatively, the coupling member can bedescribed as interconnecting less than entirely the inner or outersurface of the stent member to the graft member.

With this construction, regions of the stent member do not interfacewith the coupling member. This is believed to advantageously reduceshear stresses between the stent member and the coupling member when thestent-graft undergoes bending so that tearing of the coupling and/orgraft member can be minimized or eliminated. It is also believed thatthis arrangement minimizes the likelihood of delamination between thecoupling member and the graft. If delamination were to occur, the innerportion of the stent-graft could perceivable collapse into the vessellumen and interfere with desired blood flow. Thus, the stent-graft isbelieved to be capable of conforming to curves in a blood vessel lumenwith minimal risk of tearing the graft or coupling member, ordelamination between the stent and graft members.

According to another aspect of the invention, the coupling member issecured to the graft member without sutures. When the graft member isplaced within the stent member, for example, this arrangement eliminatesthe need for having sutures extend into the lumen formed by the graftmember and possibly interfere with blood flow. Another benefit of thisarrangement, as compared to suturing the stent to the graft member, isthat suture holes need not be placed in the graft which could adverselyaffect its integrity. The coupling member may be thermally or adhesivelybonded to the graft member.

The coupling member preferably has a generally broad or flat workingsurface as compared to filament or thread-like structures such assutures. As noted above, a preferred coupling member is in the form of aribbon. This configuration advantageously increases potential bondingsurface area between the coupling member and the graft member to enhancethe integrity of the bond therebetween. The increased bonding surfacemay facilitate minimizing the thickness of the coupling member so thatthe stent-graft lumen volume and blood flow dynamics therein can beoptimized. For example, a thicker coupling member would increase theoverall stent-graft thickness which can cause an undesirable lumendiameter reduction at the transition where the vessel lumen interfacesthe inlet of the stent-graft. This, in turn, can result in undesirableturbulent flow which possibly can lead to complications such asthrombosis.

According to a preferred embodiment of the invention, the couplingmember is arranged in a helical configuration with multiple turns. Eachof a number of the coupling member turns is spaced from the turn(s)adjacent thereto. With this construction, a generally uniformdistribution of coupling member-free stress relief zones may beachieved. Elastic wrinkling in the graft member may occur in those zonesso that the graft member can absorb stress when bent along itslongitudinal axis, for example, and resist kinking.

According to a preferred stent member construction for use with thestent-graft of the present invention, at least a portion of the stentmember includes undulations and is arranged in a helical configurationwith multiple turns. Each stent member undulation includes an apex andan open base portion. The apexes and base portions are configured so asnot to restrain one apex into the undulation in an adjacent turn andsubstantially in-phase therewith when the stent-graft is bent orcompressed. This is believed to facilitate undulation movement duringbending or compression and minimize the likelihood of stress build-upthat may cause kinking. The coupling member typically covers asubstantial portion of each undulation so as to minimize the likelihoodof the stent member apexes bending away from the graft member andinterfering with the environment or tether line which may be used tomaintain the stent-graft in a folded state before deployment. Thecoupling member also may be positioned adjacent to the apexes tominimize the likelihood of such apex movement.

According to another aspect of the invention, the end portions of thestent-member also may be enveloped between the coupling member ordiscrete coupling members and the graft member. This prevents theterminal portions of the stent and graft members from significantlymoving away from one another. For example, when the stent-member isexternal to the graft member, the terminal graft portions may flap awayfrom the stent member and possibly interfere with blood flow if theterminal coupling portions were not present.

According to another feature of the invention, the stent-graft isadvantageously manufactured by placing a cushioning layer around amandrel, assembling the stent-graft on the cushioning layer, surroundingthe mandrel mounted assembly with a multi-component member formed from aPTFE tube having a longitudinal slit and which is wrapped with anexpanded PTFE or other film or tape to compress the assembly, andheating the assembly to bond a coupling member to the graft.

The above is a brief description of some deficiencies in the prior art,and advantages and aspects of the present invention. Other features,advantages, and embodiments of the invention will be apparent to thoseskilled in the art from the following description, accompanying drawingsand appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a stent-graft constructed in accordancewith the principles of the present: invention.

FIG. 1B is an enlarged perspective view of a mid-portion of thestent-graft shown in FIG. 1A.

FIG. 1C is an enlarged perspective view of a portion of the stent-graftshown in FIG. 1A mounted on a cushioned mandrel.

FIG. 2 is a side view of an enlarged portion of the stent-graft shown inFIG. 1A.

FIG. 3A is a diagrammatic representation of a transverse section of thestent-graft of FIG. 1 prior to the coupling and graft members beingsecured to one another.

FIG. 3B is an enlarged portion of the section shown in FIG. 3A after thecoupling and graft members have been secured to one another.

FIG. 4 illustrates the stent-graft of FIGS. 1A & 1B under longitudinal,axial compression.

FIG. 5 is a sectional view of the stent-graft of FIGS. 1A and 1B takenalong line 5—5 in FIG. 4.

FIG. 6 diagrammatically shows a portion of the stent-graft of FIGS. 1Aand 1B bent along its longitudinal axis.

FIG. 7 is a perspective view of another embodiment of the stent-graft ofthe present invention having an alternate stent to graft couplingconfiguration.

FIG. 8 is a side view of an enlarged portion of the stent-graft shown inFIG. 7.

FIG. 9 is a perspective view of a further embodiment of the stent-graftof the present invention having yet another stent to graft coupling.

FIG. 10 is a side view of an enlarged portion of the stent-graft shownin FIG. 9.

FIG. 11 is a partial view of the stent-graft of FIG. 1A showing an endportion of the device.

FIG. 12 is an abstracted portion of a suitable stent and shows theconcept of torsion on a portion of that stent.

FIG. 13A diagrammatically shows a further stent-member of the presentinvention with flared ends (the coupling tape drawn back to more clearlyshow the helically wound undulating stent configuration).

FIG. 13B diagrammatically shows a further stent-member construction forsupporting the graft member.

FIGS. 14A, 14B, 14C, 14D, 14E, and 14F are plan views of unrolled stentforms suitable for use in the invention.

FIGS. 15A, 15C and 15E show procedures for folding the stent-grafts.FIGS. 15B, 15D, and 15F show the corresponding folded stent-grafts.

FIGS. 16A, 16B, and 16C diagrammatically show a procedure for deployingthe stent-grafts using an external sleeve.

FIGS. 17A and 18A are partial perspective views of folded stent-grafts.FIGS. 17B, 18C, 18B, and 18C are end views of the stent-grafts shown inFIGS. 17A and 18A in folded and open states.

FIGS. 19A, 19B, and 19C diagrammatically show a procedure for deployingthe stent-grafts shown in FIGS. 17A-17C and 18A-18C using a tether wire.

FIG. 20 show a close-up view of a stent fold line using a preferred sackknot in the slip line.

FIG. 21 is a diagrammatic perspective view of a folded stent-graft heldin a position by a tether line and a sack knot as illustrated in FIG.20.

FIGS. 22, 23, 24, and 25 are diagrammatic sequential illustrations of afurther deployment procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in detail wherein like numbers indicate likeelements, an expandable stent-graft 2 is shown constructed according tothe principles of the present invention. Although particular stent andgraft constructions will be described in conjunction with the preferredembodiments, it should be understood that other constructions may beused without departing from the scope of the invention.

Referring to FIGS. 1A and B, stent-graft 2 generally includes athin-walled tube or graft member 4, a stent member 6 and a couplingmember 8 for coupling the stent and graft members together. Preferably,the stent and graft members are coupled together so that they aregenerally coaxial.

Tubular expandable stent member 6 is generally cylindrical and comprisesa helically arranged undulating member 10 having plurality of helicalturns 12 and preferably comprising nitinol wire. The undulationspreferably are aligned so that they are “in-phase” with each other asshown in FIGS. 1A and 1B, for example. More specifically, undulatinghelical member 10 forms a plurality of undulations 14, each including anapex portion 16 and a base portion 18. When the undulations arein-phase, apex portions 16 in adjacent helical turns 12 are aligned sothat an apex portion 16 may be displaced into a respective base portion18 of a corresponding undulation in-phase therewith and in an adjacenthelical turn.

Once the undulations are aligned so that adjacent undulations in oneturn are in-phase with the undulations in the helical turns adjacentthereto, a linking member 20 may be provided to maintain the phasedrelationship of the undulations during compression and deployment, andduring bending of the stent member. In the illustrative embodiment,linking member 20 is laced or interwoven between undulations in adjacentturns of the helical member and acquires a helical configuration (See,e.g., FIGS. 1-3). Linking member 20 preferably comprises a biocompatiblepolymeric or metallic material having sufficient flexibility to bereadily folded upon itself.

Undulations 14 preferably are unconfined in that they are configured soas not to tend to inhibit the movement of flexible link 20 down betweenrespective torsion arms or lengths 22 a and 22 b. In addition, theundulations preferably are configured and arranged so that a respectiveapex portion can readily move within a corresponding undulation baseportion 18 in-phase therewith. It is believed that this constructionminimizes the likelihood of stress build-up, for example, during bendingor compression (as depicted in the lower portion of FIG. 6) and, thus,improves the kink resistance of the stent-graft.

Referring to FIGS. 3A and 3B, stent member 6 is disposed betweengenerally tubular graft member 4 and coupling member 8. The stent memberprovides a support structure for the graft member to minimize thelikelihood of the graft member collapsing during use. Although the graftmember may surround the outer surface of the stent member, it preferablyis placed within the stent member to provide a relatively smooth(wrinkles may form in the graft member between coupling member turnsduring compression) intralumental stent-graft surface as shown in thedrawings.

An important aspect of the invention is that the coupling member, whichsecures the stent member to the graft member, covers only a portion ofthe stent member. Alternatively, the coupling member can be described asis preferably interconnecting less than entirely the inner or outersurface of the stent member to the graft member (e.g., it covers lessthan all of the outer surface of the stent member when the graft memberis positioned inside the stent member). With this construction, regionsof the stent member do not interface with the coupling member when thestent-graft is an uncompressed state, for example. This is believed toadvantageously reduce shear stresses between the stent member and thecoupling member when the stent-graft undergoes bending or compression,thereby reducing the risk of tearing the graft or coupling member orcausing delamination between the stent and graft members.

The coupling member also preferably has a generally broad or flatsurface for interfacing with the stent and graft members as compared tofilament or thread-like structures such as sutures. This increasespotential bonding surface area between the coupling member and the graftmember to enhance the structural integrity of the stent-graph. Theincreased bonding surface area also facilitates minimizing the thicknessof the coupling member. It has been found that a coupling member in aform of a generally flat ribbon or tape as shown in the drawings anddesignated with reference numeral 8, provides the desired results.

As noted above, coupling member 8 preferably is in the form of agenerally flat ribbon or tape having at least one generally flatsurface. In addition, coupling member 8 is arranged in a helicalconfiguration according to the preferred embodiments illustrated in thedrawings. Referring to FIG. 2, helically arranged coupling member 8 isformed with multiple helical turns 23, each being spaced from the turnsadjacent thereto, thereby forming coupling member-free stress reliefzones 24 between adjacent turns. The coupling member also preferably isarranged to provide a generally uniform distribution of stress reliefzones 24. In the illustrated embodiments, coupling member 8 is helicallywound around the stent member with its helical turns 23 aligned with thestent member turns 12. As shown, the coupling member may be constructedwith a constant width and arranged with uniform spacing between turns.

Coupling member 8 also preferably covers a substantial portion of eachundulation so as to minimize the likelihood of the stent member apexeslifting away from the graft member and interfering with their immediateenvironment. Coupling members having widths of 0.025, 0.050 and 0.075inches have been applied to the illustrated stent member having apeak-to-peak undulation amplitude of about 0.075 inch with suitableresults. However, it has been found that as the coupling member bandwidth increases, the stent-graft flexibility generally is diminished. Itis believed that coupling member width of about one-forth tothree-fourths the amplitude of undulations 14, measured peak-to-peak, ispreferred (more preferably about one third to two thirds that amplitude)to optimize flexibility. It also has been found that by positioning oneof lateral margins of the ribbon-shaped coupling member 8 adjacent tothe apexes, e.g., in abutment with linking member 20, the couplingmember width may be reduced without significantly sacrificing apexsecurement. Varying the width of the coupling member can also result inthe adjustment of other structural properties. Increasing the width canalso potentially increase the radial stiffness and the burst pressureand decrease the porosity of the device. Increasing band width can alsodiminish graft member wrinkling between coupling member turns.

Coupling member 8 (or separate pieces thereof) also surrounds theterminal end portions of the stent-graft to secure the terminal portionsof the graft member to the support structure formed by stent member 6 asshown in FIG. 11, for example.

Although the coupling member may cover a substantial portion of eachundulation as discussed above, apex portions 16 may still move withinthe undulations in-phase therewith as shown in FIGS. 4-6 due primarilyto the flexibility of coupling and linking members 8 and 20respectively. Further, coupling member 8 may be wrapped so as to becompletely external to stent member 6 as shown in FIGS. 1-6, interwovenabove and below alternating undulations 14 as shown in FIGS. 7 and 8, orinterwoven above and below alternating undulation arms 22 a and 22 b asshown in FIGS. 9 and 10. In addition, the ribbon-shaped tape or couplingmember 8 may be axially spaced away from the apexes and linking member20 (FIGS. 9 and 10) as compared to the embodiments shown in FIGS. 1-8.This spacing provides an area 28 in which linking member 20 can freelymove without restraint, thereby reducing any resistance placed on apexesmoving into corresponding undulations during compression or bending.

The coupling member 8 may be wrapped (placed) on or interwoven with theundulations of the stent before or after it is positioned around thegraft. For example the coupling member may be placed on or interwovenwith the undulations of element 10 of FIG. 14A. As a result offluorinated ethylene propylene (FEP) coating on a surface of thecoupling member, element 10 will be bonded to the coupling member byheating. The resulting element is then configured into the stent of thisinvention. Placing or wrapping the coupling member is performed in amanner similar to that described and shown for FIGS. 1-11.

Although a particular coupling member configuration and pattern has beenillustrated and described, other configuration and/or patterns may beused without departing from the scope of the present invention. Forexample, coupling member(s) arranged in a multiple helix (e.g., a doubleor triple helix) may be used. Longitudinally extending strips of ribbonmay be used and may be preferred when the coupling member is used inconjunction with other stent member configurations.

Each undulation 14 alternatively may be described as a torsion segmentand for purposes of the following discussion will be referred to as atorsion segment 14. Referring to FIG. 12, an isolated undulation 14 isshown to facilitate the following discussion involving stent mechanicsinvolved in deployment of the device. Each torsion segment includes anapex portion 16 and two adjacent torsion arms or lengths 22 a and 22 bextending therefrom. Typically, then, each torsion arm 22 a & b will bea component of each of two adjacent torsion segments 14. When torsionsegment 14 undergoes a flexing in the amount of α apex portion 16 willflex some amount β°, torsion arm 22 a will undertake a twist of γ° andtorsion arm 22 b will undertake a twist opposite of that found intorsion arm 22 a in the amount of δ°. The amounts of angular torsionfound in the torsion arms (22 a & 22 b) will not necessarily be equalbecause the torsion arms will not necessarily be equal because thetorsion arms are not necessarily at the same angle to the longitudinalaxis of the stent-member. Nevertheless, the sum of β°+γ°+δ° will equalα°. When a value of α° is chosen, as by selection of the shape and sizeof the stent-member upon folding, the values of the other three angles(β°, γ°, δ°) are chosen by virtue of selection of number or torsionsegments around the stent, size and physical characteristics of thewire, and length of the torsion areas (22 a & b). Each of the notedangles must not be so large as to exceed the values at which the chosenmaterial of construction plastically deforms at the chosen value of α°.

To further explain: it should be understood that torsion segment 14undergoes a significant amount of flexing as the stent-member is foldedor compressed in some fashion. The flexing provides a twist to thetorsion arms (22 a & b), a significant portion of which is generallyparallel to the longitudinal axis of the stent.

The described stent-member uses concepts which can be thought of aswidely distributing and storing the force necessary to fold the tubularstent into a configuration which will fit through a diameter smallerthan its relaxed outside diameter without inducing plastic deformationof the constituent metal or plastic and yet allowing those distributedforces to expand the stent upon deployment.

Once the concept of distributing the folding or compression stressesboth into a bending component ( as typified by angle β° in FIG. 12) andto twisting components ( as typified by angle γ° and δ° in FIG. 12) anddetermining the overall size of a desired stent, determination of theoptimum materials as well as the sizes of the various integralcomponents making up the stent becomes straightforward. Specifically,the diameter and length of torsion lengths, apex portion dimensions andthe number of torsion segments around the stent may then be determined.

Referring to FIG. 13A, a stent-graft^(iv) differing from stent-graft 1in graft support structure is shown. Stent-graft 2 ^(iv) includes stentmember 6′ which is the same as stent member 6 with the exception that itincludes flared end portions 142 at one or both ends. Flared endportions 142 provide secure anchoring of the resulting stent-graft 2^(iv) against the vessel wall and prevents the implant from migratingdownstream. In addition, flared end portions 142 provide a tight sealagainst the vessel so that the blood is channeled through the lumenrather than outside the graft. The undulating structure may vary inspacing to allow the helical turns to maintain their phased relationshipas discussed above. Although a linking member between the continuoushelical turns is not shown, such structure preferably is included tomaintain the alignment of the apexes as discussed above.

The graft support structure also may be made by forming a desiredstructural pattern out of a flat sheet. The sheet may then be rolled toform a tube. The stent also may be machined from tubing. If the chosenmaterial is nitinol, careful control of temperature during the machiningstep may be had by EDM (electro-discharge-machining), laser cutting,chemical machining, or high pressure water cutting. As shown in FIG.13B, the stent-member (graft support structure) may comprise multipletubular members or sections 50, each coupled to the graft-member 4 witha coupling member as described above. Tubular members or sections 50 mayhave various construction and, thus, may be configured to have the sameconstruction as the stent-member 6 shown in FIGS. 1-11, for example.Tubular members also may be directly coupled to each other (e.g., withbridging element(s) extend between adjacent sections as would beapparent to one of ordinary skill) or, indirectly coupled to each otherthrough their interconnection with the graft member.

Referring to FIGS. 14A-F, various undulation configurations suitable forthe present invention are shown. FIG. 14A shows the sinusoidal shapedundulating member 10 described above. Adjacent torsion arms 22 a & b arenot parallel. FIG. 14B shows an undulating member 10′ having generallyU-shaped undulations or torsion members where the torsion arms aregenerally parallel. FIG. 14C shows a further variation where undulatingmember 10″ includes ovoid shaped undulations or torsion segments. Inthis variation, adjacent torsion arms 22″ a & b are again not parallel,but generally form an open-ended oval. FIG. 14D shows another variationwhere undulating member 10′″ includes V-shaped torsion members. In thisvariation, the adjacent torsion arms 120 form a relatively sharp angleat the respective apex portions. FIG. 14E shown undulating member 10^(iv) in which adjacent undulations have different amplitudes. The peaksof the large amplitude torsion segments 119 may be lined up “out ofphase” or “peak to peak” with small or large amplitude torsion segments110, 121, respectively, in the adjacent turn of the helix or may bepositioned “in phase” similar to those discussed with regard to FIGS. 1Aand B above. The configurations shown in FIGS. 14A-14E are exceptionallykink-resistant and flexible when flexed along the longitudinal axis ofthe stent-member. FIG. 14F shows a stent formed from sections 11 and 13which are connected to one another by sutures 15.

As discussed above, the stent member preferably is oriented coaxiallywith the tubular graft member. Although the stent member may be placedwithin the graft member, it preferably is placed on the outer surface ofthe graft member so that a relatively smooth graft wall interfaces withthe blood. In certain configurations, an additional graft member may beplaced on the outer surface of the stent-graft illustrated in thedrawings. When the multiple graft structure is utilized, the stentstructure should have the strength and flexibility to urge the grafttubing firmly against the vessel wall so that the graft member conformswith the inner surface of the vessel wall. In addition, the graft memberpreferably is impermeable to blood at normal or physiologic bloodpressures. The impermeability makes the stent-graft suitable forshunting and thereby hydraulically isolating aneurysms.

The scope of materials suitable for the stent and graft members and thelinking member as well as deployment mechanisms will be discussed indetail, below.

Stent Materials

The stent member is constructed of a reasonably high strength material,i.e., one which is resistant to plastic deformation when stressed.Preferably, the stent member comprises a wire which is helically woundaround a mandrel having pins arranged thereon so that the helical turnsand undulations can be formed simultaneously. Other constructions alsomay be used. For example, an appropriate shape may be formed from a flatstock and wound into a cylinder or a length of tubing formed into anappropriate shape.

In order to minimize the wall thickness of the stent-graft, the stentmaterial should have a high strength-to-volume ratio. Use of designs asdepicted herein provides stents which may be longer in length thanconventional designs. Additionally, the designs do not suffer from atendency to twist (or helically unwind) or to shorten as the stent-graftis deployed. As will be discussed below, materials suitable in thesestents and meeting these criteria include various metals and somepolymers.

A percutaneously delivered stent-graft must expand from a reduceddiameter, necessary for delivery, to a larger deployed diameter. Thediameters of these devices obviously vary with the size of the bodylumen into which they are placed. For instance, the stents of thisinvention may range in size from 2.0 mm in diameter (for neurologicalapplications) to 40 mm in diameter (for placement in the aorta). A rangeof about 2.0 mm to 6.5 mm (perhaps to 10.0 mm) is believed to bedesirable. Typically, expansion ratios of 2:1 or more are required.These stents are capable of expansion ratios of up to 5:1 for largerdiameter stents. Typical expansion ratios for use with the stents-graftsof the invention typically are in the range of about 2:1 to about 4:1although the invention is not so limited. The thickness of the stentmaterials obviously varies with the size (or diameter) of the stent andthe ultimate required yield strength of the folded stent. These valuesare further dependent upon the selected materials of construction. Wireused in these variations are typically of stronger alloys, e.g., nitinoland stronger spring stainless steels, and have diameters of about 0.002inches to 0.005 inches. For the larger stents, the appropriate diameterfor the stent wire may be somewhat larger, e.g., 0.005 to 0.020 inches.For flat stock metallic stents, thickness of about 0.002 inches to 0.005inches is usually sufficient. For the larger stents, the appropriatethickness for the stent flat stock may be somewhat thicker, e.g., 0.005to 0.020 inches.

The stent-graft is fabricated in the expanded configuration. In order toreduce its diameter for delivery the stent-graft would be folded alongits length, similar to the way in which a PCTA balloon would be folded.It is desirable, when using super-elastic alloys which also havetemperature-memory characteristics, to reduce the diameter of the stentat a temperature below the transition-temperature of the alloys. Oftenthe phase of the alloy at the lower temperature is somewhat moreworkable and easily formed. The temperature of deployment is desirablyabove the transition temperature to allow use of the super-elasticproperties of the alloy.

There are a variety of disclosures in which super-elastic alloys such asa nitinol are used in stents. See, U.S. Pat. Nos. 4,503,569 to Dotter,4,512,338 to Balko et al., 4,990,155 to Wilkoff, 5,037,427 to Harada, etal., 5,147,370 to MacNamara et al., 5,211,658 to Clouse, and 5,221,261to Termin et al. None of these references suggest a device havingdiscrete individual, energy-storing torsional members.

Jervis, in U.S. Pat. Nos. 4,665,906 and 5,067,957, describes the use ofshape memory alloys having stress-induced martensite properties inmedical devices which are implantable or, at least, introduced into thehuman body.

It should be clear that a variety of materials variously metallic,superelastic alloys, and preferably nitinol, are suitable for use inthese stents. Primary requirements of the materials are that they besuitably springy even when fashioned into very thin sheets or smalldiameter wires. Various stainless steels which have been physically,chemically, and otherwise treated to produce high springiness aresuitable, as are other metal alloys such as cobalt chrome alloys (e.g.,ELGILOY), platinum/tungsten alloys, and especially the nickel-titaniumalloys generically known as “nitinol”.

Nitinol is especially preferred because of its “super-elastic” or“pseudo-elastic” shape recovery properties, i.e., the ability towithstand a significant amount of bending and flexing and yet return toits original form without deformation. These metals are characterized bytheir ability to be transformed from an austenitic crystal structure toa stress-induced martensitic structure at certain temperatures, and toreturn elastically to the austenitic shape when the stress is released.These alternating crystalline structures provide the alloy with itssuper-elastic properties. These alloys are well known but are describedin U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700. Typically nitinolwill be nominally 50.6% (±0.2%) Ni with remainder Ti. Commerciallyavailable nitinol materials usually will be sequentially mixed, cast,formed, and separately cold-worked to 30-40%, annealed, and stretched.Nominal, ultimate yield strength values for commercial nitinol are inthe range of 30 psi and for Young's modulus are about 700 Kbar.

The '700 patent describes an alloy containing a higher iron content andconsequently has a higher modulus than the Ni—Ti alloys.

Nitinol is further suitable because it has a relatively high strength tovolume ratio. This allows the torsion members to be shorter than forless elastic metals. The flexibility of the stent-graft is largelydictated by the length of the torsion segments and/or torsion arms. Theshorter the pitch of the device, the more flexible the stent-graftstructure can be made. Materials other than nitinol are suitable. Springtempered stainless steels and cobalt-chromium alloys such as ELGILOY arealso suitable as are a wide variety of other known “super-elastic”alloys.

Although nitinol is preferred in this service because of its physicalproperties and its significant history in implantable medical devices,we also consider it also to be useful in a stent because of its overallsuitability with magnetic resonance imaging (MRI) technology. Many otheralloys, particularly those based on iron, are an anathema to thepractice of MRI causing exceptionally poor images in the region of thealloy implant. Nitinol does not cause such problems.

Other materials suitable as the stent include certain polymericmaterials, particularly engineering plastics such as thermotropic liquidcrystal polymers (“LCP's”). These polymers are high molecular weightmaterials which can exist in a so-called “liquid crystalline state”where the material has some of the properties of a liquid (in that itcan flow) but retains the long range molecular order of a crystal. Thereterm “thermotropic” refers to the class of LCP's which are formed bytemperature adjustment. LCP's may be prepared from monomers such asp,p′-dihydroxy-polynuclear-aromatics or dicarboxy-polynuclear-aromatics.The LCP's are easily formed and retain the necessary interpolymerattraction at room temperature to act as high strength plastic artifactsas are needed as a foldable stent. They are particularly suitable whenaugmented or filled with fibers such as those of the metals or alloysdiscussed below. It is to be noted that the fibers need not be linearbut may have some preforming such as corrugations which add to thephysical torsion enhancing abilities of the composite.

Linking Member Materials

Flexible link 20, which is slidably disposed between adjacent turns ofthe helix may be of any appropriate filamentary material which is bloodcompatible or biocompatible and sufficiently flexible to allow the stentto flex and not deform the stent upon folding. Although the linkage maybe a single or multiple strand wire (platinum, platinum/tungsten, gold,palladium, tantalum, stainless steel, etc.), much preferred in thisinvention is the use of polymeric biocompatible filaments. Syntheticpolymers such as polyethylene, polypropylene, polyurethane, polyglycolicacid, polyesters, polyamides, their mixtures, blends and copolymers aresuitable; preferred of this class are polyesters such as, polyethyleneterephthalate including DACRON and MYLAR and polyaramids such as KEVLAR,polyfluorocarbons such as polytetrafluoroethylene with and withoutcopolymerized hexafluoropropylene, TEFLON or ePTFE, and porous ornonporous polyurethanes. Natural materials or materials based on naturalsources such as collagen may also be used in this service.

Graft Member Materials

The tubular component or graft member of the stent-graft may be made upof any material which is suitable for use as a graft in the chosen bodylumen. Many graft materials are known, particularly known are those usedas vascular graft materials. For instance, natural materials such ascollagen may be introduced onto the inner surface of the stent andfastened into place. Desirable collagen-based materials include thosedescribed in U.S. Pat. No. 5,162,430, to Rhee et al, and WO 94/01483(PCT/US93/06292), the entirety of which are incorporated by reference.Synthetic polymers such as polyethylene, polypropylene, polyurethane,polyglycolic acid, polyesters, polyamides, their mixture, blends,copolymers, mixtures, blends and copolymers are suitable, preferred ofthis class are polyesters such as polyethylene terephthalate includingDACRON and MYLAR and polyaramids such as KEVLAR, polyfluorocarbons suchas polytetrafluoroethylene (PTFE) with and without copolymerizedhexafluoropropylene, expanded or not-expanded PTFE, and porous ornonporous polyurethanes. Especially preferred in this invention are theexpanded fluorocarbon polymers (especially PTFE) materials described inBritish Pat. Nos. 1,355,373, 1,506,432, or 1,506,432 or in U.S. Pat.Nos. 3,953,566, 4,187,390, or 5,276,276, the entirety of which areincorporated by reference.

Included in the class of preferred fluoropolymers arepolytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),copolymers of tetrafluorethylene (TFE), and perfluoro (propyl vinylether) (PFA), homopolymers of polychlorotrifluoroethylene (PCTFE), andits copolymers with TFE, ethylene-chlorotrifluoroethylene (ECTFE),copolymers of ethylene-tetrafluoroethylene (ETFE), polyvinylidenefluoride (PVDF), and polyvinyfluoride (PVF). Especially preferred,because of its widespread use in vascular protheses, is expanded PTFE.

In addition, one or more radio-opaque metallic fibers, such as gold,platinum, platinum-tungsten, palladium, platinum-iridium, rhodium,tantalum, or alloys or composites of these metals like may beincorporated into the device, particularly, into the graft, to allowfluoroscopic visualization of the device.

The tubular component may also be reinforced using a network of smalldiameter fibers. The fibers may be random, braided, knitted or woven.The fibers may be imbedded in the tubular component, may be placed in aseparate layer coaxial with the tubular component, or may be used in acombination of the two.

A preferred material for the graft and coupling members is porousexpanded polytetrafluorethylene. An FEP coating is one preferredadhesive that is provided on one side of the coupling member.

Manufacture of the Stent-Graft

The following example is provided for purposes of illustrating apreferred method of manufacturing a stent-graft constructed according tothe present invention which in this example case is the stent-graftshown in FIGS. 1-6. It should be noted, however, that this example isnot intended to limit the invention.

The stent member wire is helically wound around a mandrel having pinspositioned thereon so that the helical structure and undulations can beformed simultaneously. While still on the mandrel, the stent member isheated to about 460° F. for about 20 minutes so that it retains itsshape.

Wire sizes and materials may vary widely depending on the application.The following is an example construction for a stent-graft designed toaccommodate 6 mm diameter vessel lumen. The stent member comprises anitinol wire (50.8 atomic % Ni) having a diameter of about 0.007 inch.In this example case, the wire is formed to have sinusoidal undulations,each having an amplitude measured peak-to-peak of about 0.100 inch andthe helix is formed with a pitch of about 10 windings per inch. Theinner diameter of the helix (when unconstrained) is about 6.8 mm. Thenitinol wire may be polished if desired. If a polished wire is desired,the wire is fed through an electrolytic bath having an applied potentialto electrolytically clean, passivate and polish the wire. The polishingreduces the availability of surface nickel for extraction or corrosion.Suitable electrolytic treating materials for the bath are commerciallyavailable. One such source of a commercially available electrolytictreating material is NDC (Nitinol Devices and Components. The linkingmember can be arranged as shown in the drawings and may have a diameterof about 0.006 inch.

In this example, the graft member is porous expandedpolytetrafluorethylene (PTFE), while the coupling member is expandedPTFE coated with FEP. The coupling member is in the form of a flatribbon (as shown in the illustrative embodiments) that is positionedaround the stent and graft members as shown in FIGS. 1-3. The side ofthe coupling member or ribbon that is FEP coated faces the graft memberto secure it to the graft member. The intermediate stent-graftconstruction is heated to allow the materials of the ribbon and graftmember to merge and self-bind as will be described in more detail below.

The FEP-coated porous expanded PTFE film used to form the ribbon shapedcoupling member preferably is made by a process which comprises thesteps of:

(a) contacting a porous PTFE film with another layer which is preferablya film of FEP or alternatively of another thermoplastic polymer.

(b) heating the composition obtained in step (a) to a temperature abovethe melting point of the thermoplastic polymer;

(c) stretching the heated composition of step (b) while maintaining thetemperature above the melting point of the thermoplastic polymer, and

(d) cooling the product of step (c)

In addition to FEP, other thermoplastic polymers including thermoplasticfluoropolymers may also be used to make this coated film. The adhesivecoating on the porous expanded PTFE film may be either continuous(non-porous) or discontinuous (porous) depending primarily on the amountand rate of stretching, the temperature during stretching, and thethickness of the adhesive prior to stretching.

The thin wall expanded PTFE graft used to construct this examplecontains an inner tube of PTFE and an outer helical wrap of PTFE. Thegraft was about 0.1 mm (0.004 in) thickness and had a density of about0.5 g/cc. The microstructure of the porous expanded PTFE containedfibrils of about 25 micron length. A 3 cm length of this graft materialwas placed on a mandrel the same diameter as the inner diameter of thegraft. Advantageously, as shown in FIG. 1C, a cushioning layer 5 wasplaced on the mandrel 3 prior to placement of the graft 4. The nitinolstent member having about a 3 cm length was then carefully fitted overthe center of the thin wall graft 4 and extended to its desired length.Any struts out of phase should be placed in phase prior to applying thecoupling member.

The stent-member was then provided with a ribbon shaped coupling membercomprised of the FEP coated film as described above. The coupling memberwas helically wrapped around the exterior surface of the stent-member asshown in FIGS. 1-6. The uniaxially-oriented fibrils of themicrostructure of the helically-wrapped ribbon were helically-orientedabout the exterior of stent surface. The ribbon shaped coupling memberwas oriented so that its FEP-coated side faced inward and contacted theexterior of surface of the stent-member. This ribbon surface was exposedto the outward facing surface of the thin wall graft member exposedthrough the openings in the stent member.

Advantageously, an outer, multi-component sheath 9, formed by alongitudinally slit tube of non-adhering PTFE and an outer helical wrapof non-adhering PTFE is placed around the stent-graft-coupling memberassembly to compress the assembly onto the mandrel (FIG. 1C).Alternatively, sheath 9 may be formed by helically wrapping PTFE aroundthe stent-graft-coupling assembly without the longitudinally slit tube.

The mandrel assembly was placed into an oven set at 315° C. for a periodof 15 minutes after which the film-wrapped mandrel was removed from theoven and allowed to cool. Following cooling to approximately ambienttemperature, the mandrel, as well as the cushioning layer and outercompression tube, was removed from the resultant stent-graft. The amountof heat applied was adequate to melt the FEP-coating on the porousexpanded PTFE film and thereby cause the graft and coupling members toadhere to each other. Thus, the graft member was adhesively bonded tothe inner surface of helically-wrapped coupling member 8 through theopenings between the adjacent wires of the stent member. The combinedthickness of the luminal and exterior coverings (graft and couplingmembers) and the stent member was about 0.4 mm.

The stent-graft was then folded in order to prepare it for delivery. Toaccomplish this a stainless steel wire which was a couple of incheslonger than the stent-graft was inserted through the lumen of thestent-graft. The stent-graft was flattened and the stainless steel wirepositioned at one end of the stent-graft. A second stainless wire ofabout the same length was placed on the outer surface of the stent-graftadjacent to the first stainless steel wire. The wires were then mountedtogether into a fixture, tensioned and then rotated, thereby folding thestent-graft as shown in FIGS. 15C & D which will be discussed in moredetail below. As the stent-graft rotates it is pressed into a “C” shapedelongated stainless steel clip in order to force it to roll upon itself.The folded stent-graft is then advanced along the wire out of the clipinto a glass capture tube. A removable tether line, which is used toconstrain the stent-graft in the rolled configuration for delivery, aswill be discussed in more detail below, is applied to the stent-graft atthis point by gradually advancing the stent-graft out of the capturetube and lacing the tether line through the stent-graft structure. Afterthis step is completed, the stent-graft is pulled off of the first wireand transferred onto the distal end of the catheter shaft or tubing fordelivery.

Prior to folding, the stent-graft was cooled to about −30° C. so thatthe nitinol was fully martensitic and, thus, malleable. This is done toallow the stent-graft to be more easily folded. Cooling is accomplishedby spray soaking the graft with chilled gas such as tetrafluroethane.Micro-Dust™ dry circuit duster manufactured by MicroCave Corporation(Conn) provides suitable results. The spray canister was held upsidedown to discharge the fluid as a liquid onto the stent-graft.

Deployment of the Stent-Graft

The stent-graft may be delivered percutaneously, typically through thevasculature, after having been folded to a reduced diameter. Oncereaching the intended delivery site, it is expanded to form a lining onthe vessel wall.

When a stent-graft having torsion members, as described above, isfolded, crushed, or otherwise collapsed, mechanical energy is stored intorsion in those members. In this loaded state, the torsion members havea torque exerted by the torsion members as folded down to a reduceddiameter must be restrained from springing open. The stent-memberpreferably has at least one torsion member per fold. The stent-graft isfolded along its longitudinal axis and restrained from springing open.The stent-graft is then deployed by removing the restraining mechanism,thus allowing the torsion members to spring open against the vesselwall. The stent grafts of this invention are generally self-opening oncedeployed. If desired, an inflatable balloon catheter or similar means toensure full opening of the stent-graft may be used under certaincircumstances.

The attending physician will select an appropriately sized stent-graft.Typically, the stent-graft will be selected to have an expanded diameterof up to about: 10% greater than the diameter of the lumen at thedeployment site.

FIG. 15A diagrammatically illustrates a folding sequence for folding astent-graft constructed according to the present invention. Thestent-graft, generally designated with reference numeral 200 ispositioned about a guidewire 232 and folded into a loose C-shapedconfiguration. FIG. 15B shows a diagrammatic perspective view of theresulting folded stent-graft. FIGS. 15C & E show further foldingsequences. FIGS. 15D & F show diagrammatic perspective views of theresulting folded stent-grafts showing the rolled and triple lobedconfigurations, respectively. The rolled configuration is preferred.

FIGS. 16A-16C diagrammatically illustrate deployment procedures for thepresent invention. FIG. 16A shows an example target site having anarrowed vessel lumen. A guidewire 208 having a guide tip has beendirected to the site using known techniques. The stent-graft 210 ismounted on guidewire tubing 212 inside outer sliding sheath 214 afterhaving been folded in the manner discussed above. The outer slidingsheath 214 binds the compressed stent-graft 210 in place until released.

FIG. 16B shows placement of the stent-graft 120 at the selected site bysliding the stent-graft over the guidewire all together with theguidewire tubing 212 and the outer sliding sheath 214. The stent-graftis deployed by holding the guidewire tubing 212 in a stationary positionwhile withdrawing the outer sliding sheath 214. FIG. 16B shows thestent-graft partially deployed, while FIG. 16C shows the stent-graftfully deployed after the guidewire tubing and the outer sliding sheathhave been fully retracted.

FIGS. 17A-C, 18A-C, and 19A-C show deployment variations for deploying astent-graft constructed according to the present invention. Thesemethods involve the use of a control line or tether line which maintainsthe stent or stent-graft in a folded configuration until release.

Referring to FIGS. 17A & B, diagrammatically represented stent-graft 302is shown folded about guidewire 304 so that, when deployed, theguidewire 304 is within stent-graft 302. A tether wire 306 is passedthrough loops 308 which preferably are formed by pulling the linkingmember discussed above away from the stent structure. When tether wire306 is removed by sliding it axially along the stent-graft and out ofloops 308, the stent-graft unfolds into a generally cylindrical shape.(FIG. 17C). Referring to, FIGS. 18A & B stent-graft 302 is shown in arolled pre-deployment configuration. In this case, guidewire 304 isinside the stent. When expanded by removal of tether wire 306, thestent-graft assumes the form shown in FIG. 18C.

FIGS. 19A-C diagrammatically show additional procedures for deploying astent-graft of the present invention using a percutaneous catheterassembly 314. Referring to FIG. 19A catheter assembly 314 has beeninserted to a selected site within a body lumen. Stent-graft 312 isfolded about guidewire 319 and guidewire tube 318 held axially in placeprior to deployment by distal barrier 320 and proximal barrier 322. Thedistal and proximal barriers typically are affixed to the guidewire tube318. Tether wire 306 is extends through loops 308 proximally through thecatheter assembly's 314 outer jacket 324 through to outside the body.FIG. 19B shows partial removal of tether wire 306 from loops 308 topartially expand the stent-graft 312 onto the selected site. FIG. 19Cshows complete removal of the tether wire, the loops and retraction ofthe catheter assembly 314 from the interior of the stent-graft which isfully expanded.

FIG. 20 shows a close-up of a stent fold line having the familiarherringbone pattern of the preferred “sack knot” used to close the foldin the stent. This knot is the one used to hold, e.g., burlap sacks offeed grain closed prior to use and yet allow ease of opening when thesack is to be opened. In this variation, the slip line has a fixed end320 and a release end 322. Loops of the slip line pass through theeyelets 324 on the side of the stent fold associated with the fixed end320 and are held in place by eyelets 326 on the side of the stent foldassociated with the release end 322. The fixed end 320 is not typicallytied to the stent so to allow removal of the slip line after deployment.The eyelets 324 and 326 are desirable but optional. The eyelets 324 and326 may be wire or polymeric thread or the like tied to the stentstructure at the edge of the stent fold. If so desired, the loops may bedispensed with and the slip line woven directly into the stentstructure. The self-expanding stent may be deployed by pulling axiallyon release end 322 as shown by the arrow in the drawing.

FIG. 21 is a diagrammatic perspective view of a folded stent-graft usingthe knot shown in FIG. 20. FIG. 21 shows the use of a single stent foldsimilar in configuration to those described above. As was shown in FIG.20, the fixed end portion 320 of the slip line is associated with a rowof eyelets 324 which preferably are formed by pulling local portions oflinking member 20 away from the fold line, threading the slip linetherethrough and then releasing the respective portion of the linkingmember. Alternatively, the eyelets may be tied or otherwise fixed to thestent. The release end 322 is associated with the other row of eyelets326.

Although stent-graft deployment is described using a catheter forpercutaneous delivery, it should be understood that other deploymenttechniques may be used. The folded stent-graft may also be deployedthrough artificial or natural body openings with a sheath or endoscopicdelivery device, for example, and perhaps, without a guidewire.Similarly, the stent-graft may be delivered manually during a surgicalprocedure.

The stent-graft of the present invention may be used, for example, toreinforce vascular irregularities and provide a smooth nonthrombogenicinterior vascular surface for diseased areas in blood vessels, or toincrease blood flow past a diseased area of a vessel by mechanicallyimproving the interior surface of the vessel. The inventive stent-graftis especially suitable for use within smaller vessels between 2 mm and 6mm in diameter but is equally suitable for significantly larger vessels.The inventive stent-graft may be self-expanded so that it may bepercutaneously delivered in a folded state on an endovascular catheteror via surgical or other techniques and then expanded. The stent-graftconstruction described above also provides a variable lengthstent-graft. This is especially advantageous during implantationprocedures.

Currently, it is difficult for a physician to accurately determineanatomical distances due to vessel tortuosity in different planes whichoften occurs in aorta/iliac aneurysmal disease. Also, it is importantfor the physician to accurately measure distances when placing anendovascular stent-graft so the entire aneurysmal length is covered, yetimportant vessel branches are not occluded. The stent-graft design ofthe present invention allows the physician to adjust its length duringdeployment allowing more accurate placement of the device.

The following example illustrates the steps involved in placing avariable-length stent-graft into a patient's anatomy. In this example,stent-graft is a single tubular design, placed into the thoracic aorta70, and will be located between the renal arteries and the T-7 artery.The direction of deployment will be from renals ‘upstream’to the T-7artery. The device will be supplied in its longest state with shorteningcapability during deployment (the inverse where a copressed stent-graftis deployed also is possible).

The physician estimates the length required, and chooses a device whichis at least as long, and usually slightly longer than the estimatedlength.

The stent-graft is inserted through an introducer as is conventional inthe art. It is advanced until its distal ends 2 a is located as desirednear the renal arteries (72) (FIG. 22). At this point, the proximal endof the stent-graft would be located at or past the T-7 artery (74).

The stent-graft deployment is initiated slowly, distal to proximal(‘downstream to upstream’) (FIG. 23) while watching the proximal endlocation on fluoroscopy.

As needed, the delivery catheter 76, which is of conventionalconstruction, would be pulled toward the operator, shortening thestent-graft to keep the proximal end in the correct location. Thisshortening can occur as long as the portion of the stent-graft beingcompressed is within the aneurysm 78.

Once the proximal end is correctly located (FIG. 24), the stent graft isfully deployed, and the delivery catheter is removed (FIG. 25).

Throughout this application, various publications, patents and patentapplications are referred by an identifying citation. The disclosures ofthese publications, patents and published patent applications are herebyincorporated by referenced into this application.

The above is a detailed description of a particular embodiment of theinvention. The full scope of the invention is set out in the claims thatfollow and their equivalents. Accordingly, the claims and specificationshould not be construed to unduly narrow the full scope of protection towhich the invention is entitled.

What is claimed is:
 1. A process for making a stent graft comprising:(a) placing a graft member around a mandrel; (b) positioning anundulating stent member having an inner surface and an outer surfacearound said graft member; and (c securing said stent member to saidgraft member with a ribbon having multiple spaced apart strips, whichribbon is adhered to at least one of the inner and outer surfaces ofsaid stent member, to form a stent-graft assembly.
 2. The processaccording to claim 1 further comprising the step of: (a1) prior to step(a), placing a cushioning layer around the mandrel.
 3. The processaccording to claim 1, wherein said securing step comprises helicallywrapping the ribbon around the stent member whereby adjacent turns ofthe helically wrapper ribbon are spaced from one another and form saidspaced apart strips.
 4. The process according to claim 2, wherein saidsecuring step comprises helically wrapping the ribbon around the stentwhereby adjacent turns of the helically wrapper ribbon are spaced fromone another.
 5. The process according to claim 2 wherein the ribbon isbonded to an outer surface of the graft member.
 6. The process accordingto claim 1 further comprising the step of: (d) placing a sheath aroundthe assembly of step (c) to form a compressed assembly.
 7. The processaccording to claim 6 further comprising the step of: (e) heating theassembly of step (d) to adhere the ribbon to the graft member.
 8. Theprocess according to claim 4 further comprising: (d) placing a tubularsheath having a longitudinal slit around the assembly of step (c); and(e) helically wrapping a film around the sheath to compress theassembly.
 9. The processing according to claim 6 wherein the sheathincludes a helical wrapping of PTFE film.
 10. The stent-graft of claim 6wherein one side of said ribbon has a coating of fluorinated ethylenepropylene polymer.